This invention relates to a method and apparatus for longitudinally slitting metal strip. More particularly, this invention relates to slitting light or heavy gauge strip material under tension to wind tighter and larger coils of slit strip material.
Generally, slitting of light gauge metal is accomplished with known techniques using zero tension through the slitter. Such devices provide for a loop of strip material before and after the slitter and a driven slitter having knives which transport the strip material through the slitter as part of the operation. A problem associated with slitting metal strip under zero tension is that tight coils of slit strip cannot readily be wound on the take-up winder or reel. Through the use of "slip cores" in the take-up winder and through specially-adapted bridle roll arrangements, this problem has been alleviated; however, there is still the problem of unequal loops of slit material between the slitter and winding reel.
The problem of unequal loops of slit material results from any differential speeds of the individual strips slit from the strip material. Unequal loops may result from overrolled and thus thinner gauge strip at the edges of the unslit strip. The problem is particularly acute for lighter gauge metal strip. Smaller diameter edge coils result in differential speeds of individual strips which form unequal loops of slit material. Under extreme conditions, unequal loops can have a differential of several hundred feet and require a looping pit of impractical depth.
By slip cores, it is meant that the take-up winder includes individual friction discs mounted on a winder shaft. Friction pressure is provided through a hydraulic cylinder controlled with variable hydraulic pressure to provide the desired tension. The slit material strips are attached to individual friction discs (or slip cores) which allow relative motion between individual coils. Such slip cores used with slitting metal strip are presently available from Strouss Industries, Inc.
Tighter coils of strip material can be produced by placing the strip under tension during windup and/or slitting. It is known, however, that pull-through slitting of strip material is not practical because of the mechanical drag of the slitter and the minimal contact between the slitter knives and the metal strip material. Known techniques for slitting material under tension are shown in the patent art. U.S. Pat. No. 1,355,104, issued Oct. 5, 1920, discloses a slitting machine primarily for paper which uses a driven roller to draw paper through shears at a constant speed. One of the slitting members is driven and frictionally drives a seccnd slitting member.
U.S. Pat. No. 2,251,282, issued Aug. 5, 1941, relates to a machine to slit or cut ribbons from a fabric web pulled under tension through the cutters for the purpose of eliminating drag on the fabric at the point of cutting. Shafts or rolls located after the cutters control the advance of the fabric through the cutters, as well as drive the cutters.
U.S. Pat. No. 3,803,959, issued Apr. 16, 1974, discloses a belt slitting apparatus which slits primarily elastic material under tension or stretching and provides adjustable tension longitudinally through feed and guide rolls. The apparatus includes driven supply and take-up rolls and driven feed rolls before the slitter and driven guide rolls after the slitter. Reversibility of the supply and take-up rolls is used to stretch and control the tension of the material at any given time.
There is a need for a method and apparatus for winding tight coils of slit metal strip materials of light or heavy gauge. It is desirable that the slit metal strip be put under tension while being wound. Furthermore, an objective is for slitting of the metal strip under tension and coil winding under tension without the problems of the prior art, such as by eliminating the problem of unequal loops of slit material. A method and apparatus which can provide a more efficient, less complicated and faster slitting operation and which can solve the deficiencies of the prior devices is an objective.